Reduction of copper corrosivity of sweet oils



United States PatetitO 5 REDUCTION OF COPPER CORROSIVITY OF 7 SWEET OILSNo Drawing. Application March 12, 1954, Serial No. 415,947

9 Claim (Cl. 196-32) This invention relates to a method for reducing.the corrosivity to copper of sweet oils wherein the corrosivity iscaused by organic sulfur compounds and/ or free-sulfur.

Although the doctor process is probably the most commonly used processfor converting the mercaptan in sour petroleum distillates todisulfides, it has some drawbacks.

Frequently corrosive sulfur is present in the sweet oil. As the qualityrequirements of oils has been raised, the presence of corrosive sulfuris more and more deleterious to commercial sale of doctor sweetenedpetroleum distillates. Although it is possible, by careful control ofconditions, to avoid the formation of excessively corrosive oil, upsetsin conditions often result in the production of considerable quantitiesof sweet oil which does not meet copper corrosion specifications.Usually this oil is dumped to a product which has a lower quality demandor is recycled to the sweetening zone. Both of these expedients have aneconomic penalty.

Oils sweetened by the copper chloride process frequently are corrosiveto copper owing to the presence of free-sulfur derived by an oxidationof hydrogen sulfide present in the oil. Hypochlorite sweetened oils areoften corrosive to copper. I

An object of the invention is a process which includes sweetening andproduces a sweet oil of good copper corrosion quality. Another object isthe treatment of a doctor sweetened oil of unsatisfactory coppercorrosion quality to improve corrosivity as measured by the copper striptest. Other objects will be apparent in the course of the detaileddescription.

It has been found that a sweet oil which contains corrosiveorganic-sulfur compounds and/or free-sulfur can be improved with respectto corrosivity to copper by contacting the oil with water solublealkanolamine in an amount sufficient to form two distinct phases for atime suflicient to remove an appreciable amount of these sulfur bodies,and separating an oil of improved copper corrosivity from thealkanolamine phase. The preferred alkanolamine is triethanolamine andthe preferred agent is an aqueous solution of triethanolamine containingbetween about 2 and 15 volume percent of triethanolamine.

The hydrocarbon oil feed to the corrosion improvement process of thisinvention may be any liquid hydrocarbon oil which is corrosive to copperowing to the presence of organic-sulfur compounds and/or freesulfur, andwhich is essentially free of mercaptans as determined by the doctor testor has a mercaptan number of less than 1. The process is particularlysuitable for the treatment of petroleum distillates boiling below about750 F. Examples of these distillates are industrial naphthas, kerosene,diesel oil, heater oil, gas oil, etc. The process may be used ondistillates obtained by the fractional distillation of crude petroleumor on distillates obtained from various conversion processes such asthermal cracking, catalytic cracking, reforming in the presence ofhydrogen, etc. Sour petroleum distillates boiling in theheavier-than-gasoline range, i. e., between about 325 2,771,405 PatentedNov. 20, 1956 and 650 F., e. g., a heater oil boiling between about 330and 575 R, which have been sweetened by the doctor process, are aparticularly suitable feed.

The oil may be corrosive to copper either due to the presence ofcorrosive organic-sulfur compounds and/or free-sulfur which are notremoved in the sweetening procedure, or due to the formation of thesecorrosive bodies during the sweetening procedure. For example: A copperchloride sweetened oil may be corrosive because freesulfur developed instorage from the oxidation of H28 is not removed in the sweeteningoperation. A hypochlorite sweetened industrial naphtha may be corrosiveeither because of the presence of free-sulfur developed prior tosweetening or because corrosive bodies are developed in the sweeteningprocedure. Doctor sweetened oils usually develop corrosiveness in thesweetening.

Since doctor sweetened oils are most prone to being corrosive, thissweetening process-is described in some detail. The doctor solution ismade up of an aqueous solution of an alkali metal hydroxide and thereaction product of litharge and the alkali metal hydroxide. The amountof free-alkali metal hydroxide present in the doctor solution may bebetween about 5 and 30 weight percent, usually between about 10 and 15%.The plumbite content is commonly given in terms of the percent of PbOtheoretically present. This content for a fresh doctor solution isusually between between about 1.5 and 2.5

boiling furnace oil, temperatures as much as 150 F. or

higher may be used. Still another limitation on the contactingtemperature may be color formation in the oil, e. g., some kerosenesrapidly develop color bodies when exposed for prolonged times attemperatures above about 120 F.

The amount of doctor solution utilized usually is between about 2 andabout 50 volume percent based on sour distillate. More usually, theusage is between about 3 and about 15 volume percent.

Free-sulfur is added to the contacting zone to effect the sweetening.Frequently more than the theoretical quantity of 0.5 mol per each mol ofmercaptan sulfur present in the sour oil is needed. The use of thetheoretical quantity of free-sulfur does not always produce an oil thati s sweet to the doctor test; this is particularly true withheavier-than-gasoline distillates. The amount of excess free-sulfurnecessary varies with the sour oil charged and theoperating conditions.In general the higher boiling the sour oil, the, more excess sulfur thatis needed to produce a sweet product.

Frequently, in addition to the use of free-sulfur, frecoxygen isintroduced into the sweetening zone. The presence of free-oxygen has afavorable effect on the usage of free-sulfur and also helps to convertsome of the PbS formed in the sweetening reaction to the solubleplumbite formed. In general, the amount of free-oxygen added is betweenabout and 300% of that theoretically needed to convert the PbS.

The amines used in the corrosion improvement procedure of this inventionare the water-soluble alkanolamines. The term water soluble is intendedto include those alkanolamines which are sufliciently soluble to have abeneficial elfect. Preferably the alkanolamines should be soluble to theextent of at least about 2 volume percent based on doctor solution. Themost suitable alkanolamines are those wherein not more than 3 carbonatoms are present in each alkyl group, or conversely, wherein each alkylgroup contains from 2 to 3 carbon atoms. Exarnples of thesealkanolamines are mono-, diand triethanolamine and the propanolamines.

Although the pure or commercial grade alkanolamines are the mosteffective agents, it is usually more economical to use dilute solutionsof these alkanolamines. The dilute solution may consist essentially ofthe alkanolamine and water, or it may consist essentially ofalkali-metal hydroxide, water and alkanolamine, or it may consistessentially of doctor solution (fresh or spent) and alkanolamine. Theaqueous solution may contain about 2 volume percent or more. In general,it is preferred to use as the agent an aqueous alkanolamine solutioncontaining between about 2 and 15 volume percent of alkanolarnine,preferably triethanolamine.

The amount of alkanolamine agent utilized is at least enough to form aseparate phase in the contacting zone. The amount used is dependent inpart on the amount of alkanolamine present in the agent. In general,between about 2 and about 100 volume percent of alkanolamine agent isused based on sweet distillate charged to the contacting zone. Moreusually, the usage is between about 2 and 15 volume percent.

The temperature of contacting is usually at about atmospherictemperature. Higher temperatures may be used although in generaltemperatures in excess of about 150 F. are not necessary. In general,the temperature of contacting is between about 60 and about 150 F., andpreferably about 100 F.

The contacting is carried out for a time suflicient to improve thecopper corrosivity of the oil. The minimum time of contacting is relatedto the temperature of contacting. Roughly, the higher the temperature,the lower the corresponding contacting time. Also, the amount ofalkanolamine used has abearing on the contacting time. In general, thetime of contacting should be between about l5 minutes and 90 minutes.When operat-. ing at about 100 F., a suitable time is between about 30and 45 minutes.

The results obtainable with the process are illustrated by the followingworking examples. It is to be understood that these examples areillustrative only and do not limit the sphere of usefulness of theprocess.

EXAMPLE A In this example, the sweet oil was produced by doctorsweetening a heavy naphtha'fraction which had the followingcharacteristics:

API gravity 46- RVP 0.5 Sulfur, weight percent 0.1 ASTM, F.:

Initial 330 343 50% 370 90% 428 Max. 460

The 'corrosiveness of the sweet oil was determined by.

the Bolt copper strip technique which is described in the Oil and GasJournal of August 9, 1 9 47 nique, a copper strip is immersed for threehours in the In this. tech-.

. il which s mai tain d a a em ture f 212 ,F- In this technique aperfect strip is assigned the number 0." The higher the number assignedto the strip, the more corrosive the oil. In run 1 the sweet oil asprepared above had a copper strip of 7,

The eifect on copper strip of contacting the sweet oil with alkanolaminewas studied using triethanolarnine. The sweet oil was contacted with 10volume percent of agent for 45 minutes at a temperature within therange, -100 F. The sweet treated oil was decanted from the lowertriethanolamine agent phase and water washed to remove agent. Forpurposes of' comparison, two runs were carried out using aqueous sodiumhydroxide containing 10 weight percent of caustic. One run was carriedout contacting the sweet oil with the aqueous sodium hydroxide alonejAnother run was carried out using aqueous sodium hydroxide containing 5volume percent of triethanolamine.

The results of these tests are set out in Table I.

Table I Copper Agent Strip Number none 7 100% TEA 4 5% TEA; water 5 10%aqueous NaOH 7 5% TEA; 95% (10% aqueous NaOll) 5 EXAMPLE B In thisexample, the sour oil was a kerosene having the followingcharacteristics:

API gravity 43.4 Sulfur, weight percent. 0.09 ASTM distillation, F.:

Initial 344 10% 378 50% 426 73, Max 513 This sour kerosene was sweetenedunder conditions very similar to that of Example A except that in thiscase the free-sulfur usage to obtain a sweet product was 226% in excessof theory.

The sweet kerosene was contacted with the same agents as used in theruns of Example A. In this example the sweet kerosene was contacted withthe. agent for 30 minutes at a temperature range between and F. Theresults of these tests are set out in Table II.

T able II Copper Run No. Agent Strip Number none H 9 100% TEA 6 5% TEA;95% water." 7H 10% aqueous NaOH 9 5% TEA; 95% (10% aqueous NaOH) 7 tivein improving the corrosivity of kerosene as for a heavy naphtha, i. e.,a reduction in copper strip number of about 3 units.

It is to be understood that the contacting of the sweet oil and thealkanolamine agent may be any of the various methods known to the art.For example, the contacting may be carried out batch-wise in a singleoperation followed by gravity settling and decantation from a singlevessel. Or, the contacting may be carried out in a continuous mannerusing a tower type of contactor. The agitation in the contacting zonemay be imparted by air blowing, orifice mixers, or by mechanicalagitation.

Thus having described the invention what .is claimed is:

1. A process for improving the copper corosivity of a doctor sweetenedoil which comprises (1) intimately contacting a sour petroleumdistillate boiling in the heavierthan-gasoline range with doctorsolution and with freesulfur in an amount suificient to sweeten saiddistillate, at a temperature between about 60 and 175 F., for a timesufficient to substantially sweeten said distillate, (2) separating saidsubstantially sweet distillate from doctor solution, (3) contacting saidsubstantially sweet distillate with Water soluble alkanolamine agent inan amount suflicient to form separate distillate and alkanolaminephases, at a temperature between about 60 and about 150 F., for a timebetween about 15 minutes and 90minutes and (4) separating a sweetdistillate of improved copper corrosivity from an alkanolamine agentphase.

2. The process of claim 1 wherein said agent is triethanolamine.

3. The process of claim 1 wherein said alkanolamine is diethanolamine.

4. The process of claim 1 wherein said alkanolamine is monoethanolamine.

5. The process of claim 1 wherein said alkanolamine is propanolamine.

6. The processof claim 1 wherein said distillate is a kerosene.

7. The process of claim 1 wherein said distillate is a heater oil.

8. The process of claim 1 wherein said alkanolamine agent usage isbetween about 2 and about volume percent, based on distillate.

9. The process of claim 1 wherein said alkanolamine agent consists ofbetween about 2 and 15 volume percent of triethanolamine and theremainder essentially water.

References Cited in the file of this patent UNITED STATES PATENTS1,962,181 Eglofi June 12, 1934 2,238,201 Wilson et al Apr. 15, 19412,258,249 Johnstone Oct. 7, 1941 2,309,871 Schulze et a1 Feb. 2, 19432,311,342 Kerns et al Feb. 16, 1943 2,578,602 Rosenstein Dec. 11, 1951

1. A PROCESS FOR IMPROVING THE COPPER COROSIVITY OF A DOCTOR SWEETENEDOIL WHICH COMPRISES (1) INTIMATELY CONTACTING A SOUR PETROLEUMDISTILLATE BOILING IN THE HEAVIERTHAN-GASOLINE RANGE WITH DOCTORSOLUTION AND WITH FREESULFUR IN AN AMOUNT SUFFICIENT TO SWEETEN SAIDDISTILLATE, AT A TEMPERATURE BETWEEN ABOUT 60* AND 175* F., FOR A TIMESUFFICIENT TO SUBSTANTIALLY SWEETEN SAID DISTILLATE, (2) SEPARATING SAIDSUBSTANTIALLY SWEET DISTILLATE FROM DOCTOR SOLUTION, (3) CONTACTING SAIDSUBSTANTIALLY SWEET DISTILLATE WITH WATER SOLUBLE ALKANOLAMINE AGENT INAMOUNT SUFFICIENT TO FORM SEPARATE DISTILLATE AND ALKANOLAMINE PHASES,AT A TEMPERATURE BETWEEN ABOUT 60* AND ABOUT 150* F., FOR A TIME BETWEENABOUT 15 MINUTES AND 90 MINUTES AND (4) SEPARATING A SWEET DISTILLATE OFIMPROVED COPPER CORROSIVITY FROM AN ALKANOIAMINE AGENT PHASE.